powerpc/85xx: Add support for P2020RDB board

Add support for the P2020RDB reference board from Freescale.

Overview of P2020RDB platform
	- DDR
	  DDR2 1G
	- NOR Flash
	  16MByte
	- NAND Flash
	  32MByte
	- 3 Ethernet interfaces
	  1) etSEC1
		- RGMII
		- connected to a 5 port Vitesse Switch(VSC7385)
		- Switch is memory mapped through eLBC interface(CS#2)
		- IRQ1
	  2) etSEC2
		- SGMII
		- connected to VSC8221
		- IRQ2
	  3) etSEC3
		- RGMII
		- connected to VSC8641
		- IRQ3
	- 2 1X PCIe interfaces
	- SD/MMC ,USB
	- SPI EEPROM
	- Serial I2C EEPROM

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>